where \(T_{max}=max \lbrace T_{k}\rbrace \) .
RPD can quantify the complexity of the phase space. However, it can not measure the order of complexity. This is done by a RPD based entropy called Normalized Recurrence period density entropy (NRPDE).
Recurrence periodic entropy (RPDE) of the reconstructed phase space, where the points are independently identically distributed is defined by utilizing the concept of Shannon entropy [1]}. Thus, RPDE is given by
\(H=-\sum _{k=1}^{T_{max}}P(T_{k}) \log P(T_{k}).\) 
